Cardiovascular and Cerebrovascular Control on Return from ISS (CCISS) - 11.22.16

Science Objectives for EveryoneCardiovascular and Cerebrovascular Control on Return from ISS (CCISS) will study the effects of long-duration space flight on crewmembers' heart functions and their blood vessels that supply the brain. Learning more about the cardiovascular and cerebrovascular systems could lead to specific countermeasures that might better protect future space travelers. This experiment is collaborative effort with the Canadian Space Agency.

Science Results for Everyone
Can space break your heart, or hurt your head? Cardiovascular and Cerebrovascular Control on Return from ISS (CCISS) aims to find out, testing long-duration space flight’s effects on the heart and blood vessels supplying the brain. Changes observed are less than expected, suggesting that current exercise equipment and training regimens have astronauts well-prepared for return to Earth. However, scientists did see problems in blood vessels supplying the brain, increased reactivity to carbon dioxide, and evidence showing thickened cerebral arteries. Additional research is needed to determine whether these changes predict health complications from long-duration space flight.

The following content was provided by Richard Lee Hughson, Ph.D., and is maintained in a database by the ISS Program Science Office.

For crewmembers' health, the need to be able to maintain blood pressure immediately after returning to Earth is essential.

To obtain information on the baroreflex stability (blood pressure regulation) of ISS crewmembers an electrocardiogram and blood pressure data will be gathered prior to flight, inflight and postflight.

In addition to the electrocardiogram and blood pressure data, a lower body negative pressure (LBNP) session will be conducted preflight and postflight. The level of lower body suction will be gentle and short duration. The resulting stress on the body will be less than simply standing up in 1G.
Other data collected during the LBNP session will be brain, brachial artery, and aortic blood flows. These flows are all done non-invasively with ultrasound. Arm vein pressure, blood pressure, electrocardiogram, breathing rate and the amount of carbon dioxide expired will also be measured.
The data gathered during this investigation will lead to countermeasures to help crewmembers maintain sufficient blood pressure after long duration missions.

This study will provide a basis for studies of individuals who are susceptible to fainting in the upright posture.

Description
The ability to maintain arterial blood pressure and brain blood flow immediately on return to Earth after prolonged space flight is one of the most critical factors for crew health and safety. Although the heart rate component of the arterial baroreflex is impaired on return from space, this is not in itself a critical issue as crewmembers who are about to faint normally have markedly elevated heart rate. Rather, their inability to maintain blood pressure appears to be related to inadequate increases in peripheral vascular resistance. This study will incorporate a new methodology that determines the simultaneous gains of the arterial and cardiopulmonary baroreflexes in the control of peripheral vascular resistance.

A series of six objectives have been identified that will allow a more complete understanding of any alteration in cardiovascular or cerebrovascular responses following long duration space flight. The first two will be addressed with very brief inflight experiments that monitor the heart rate component of the arterial baroreflex and the relationship between heart rate variability and physical activity as indicators of autonomic nervous system control. The remaining objectives will be evaluated during a 32-minute test protocol conducted pre- and immediately postflight. During this test period, the central vein compliance will be monitored. In addition, the arterial and cardiopulmonary baroreflexes will be monitored during experiments that use an optimized schedule of lower body negative pressure (LBNP) to manipulate arterial and central venous blood pressures. Within these same experimental sessions assessments of cerebrovascular responsiveness to changes in arterial blood pressure and arterial partial pressure of carbon dioxide (CO2). It is anticipated that the ability to regulate blood pressure through baroreflex control of blood vessel constriction will be impaired after space flight. Similarly, it is expected that brain blood flow will be more sensitive to changes in arterial blood CO2 and, thus, will not be as tightly regulated after space flight.

Space Applications
The information derived from this study will help to better understand the effects of spaceflight on cardiovascular and cerebrovascular functions. By gaining increased knowledge of the specific components of the cardiovascular and cerebrovascular systems that deviate from the normal Earth-baseline responses, it will be possible to recommend specific countermeasures that might better protect future space travelers from complications that could put them at risk on return to the effects of gravity as will occur on re-entry to Earth or landing on the moon or Mars.

Earth Applications
The risk of fainting and falling is increased in older adults. Falls are very serious because they often cause fracture of the hip which is a major cause of prolonged disability, loss of independence and unfortunately for a high percentage of individuals the complications from the fracture will lead to death. Gaining improved knowledge of the mechanisms of loss of blood pressure and the warning signs that might predict risk will reduce the incidence of fainting and falls in the elderly.

Operational Requirements and Protocols
A total of 6 long-duration crewmembers are needed as subjects for the experiment. Baseline data for each subject will be collected at L-30 (Launch minus 30 days) for the Baro Study, 24-hr Heart Rate Study, and LBNP protocol. Baseline data will also be collected at R+1 (Return plus 1 day) for the Baro and 24-hr Heart Rate Studies and R+0 (U.S.) or R+1 (Russia) for the LBNP protocol.Crewmembers will perform CCISS operations on FD+14 (+7) (Flight Day 14) and R-14 (-7). During Day 1 operations the crewmember will don and activate the Actiwatches, CBPD, and Holter Monitor and conduct a 10-minute Baro Study. During the Baro Study, the crewmember will breathe normally for 5 minutes and then breathe at a set pace for 5 minutes. The crewmember will doff the CBPD after the conclusion of the Baro Study. The Actiwatch and Holter Monitor are worn to collect data during the 24-hr Heart Rate Study. Day 2 operations consist of the crewmember downloading data from the 24-hr Heart Rate Study and doffing the hardware.

Early evidence from long-duration flights indicates general cardiovascular fitness reduction, along with chronic elevations in arterial blood pressure in the brain and elevated inspired carbon dioxide (CO2) compared with normal upright posture on Earth. Recent studies investigated the spontaneous blood pressure feedback and markers of cardiovascular control, changes in heart rate (HR), as well as dynamic autoregulation of brain blood flow and CO2 responsiveness in astronauts living for 2–6 months on the ISS.

Overall, there was no change in indicators of cardiovascular stability during long-duration space flight and only relatively small changes postflight at rest in the seated position. Inflight measurements of heart rate, blood pressure, and blood pressure regulation versus preflight revealed no significant changes. Very small increases in resting heart rate and a 25–34% reduction in the arterial blood pressure reflex response postflight reflected relatively modest levels of decreased cardiovascular muscle tone and fitness. It was also found that astronauts maintained their preflight heart rate during daily activities while living on the ISS (Fraser et al. (2012).

These postflight changes suggests that while the current countermeasures on ISS maintain cardiovascular stability in resting conditions in space; key aspects of cardiovascular health with potential long-term consequences are not yet protected (Hughson 2012)

Studies have shown a consistent impairment of dynamic cerebrovascular autoregulation and CO2 reactivity in astronauts chronically exposed to elevated atmospheric CO2 from long-duration space flight; however, there were between-person differences in the magnitude of impairment. Evidence also suggests possible cerebrovascular consequences, such as thickening of the cerebral arteries, from prolonged elevation in cerebral blood pressure. It is unclear at the moment whether these changes have pathophysiological significance associated with the complications in vision attributed to increased intracranial pressure. Future studies should investigate in-depth pre- to postflight changes in cerebral blood flow and CO2 reactivity to determine whether they are predictors of health complications resulting from long-duration space flight (Zuj et al. 2012).

The LBNP Chamber is a simple box design that facilitates entry by the astronaut - a neoprene skirt is secured around the waist and to the front opening of the Chamber. A standard vacuum cleaner controlled by variable voltage output rheostat regulates suction. Image courtesy of NASA.+ View Larger Image

NASA Image: ISS015E14753 - Expedition 15 Flight Engineer Clay Anderson is seen here working with an Actiwatch reader and computer during hardware setup for the Cardiovascular and Cerebrovascular Control on Return from the International Space Station (CCISS) experiment in the U.S. Laboratory, Destiny. The Continuous Blood Pressure Device (CBPD) is also visible in the background.+ View Larger Image

NASA Image: ISS015E14753 - ESA astronaut Clayton Anderson working with a Continuous Blood Pressure Device (CBPD) and computer during hardware set-up for the Cardiovascular and Cerebrovascular Control on Return from the International Space Station (CCISS) experiment.+ View Larger Image